Absorption of gaseous cell product in cell liquor apparatus

ABSTRACT

The efficiency of electrolytic cells in which a gaseous cell product reacts with a component of the cell liquor or a reagent added to the electrolytic cell, may be substantially improved by the insertion of gas-dispersing means above the electrodes of the electrolytic cell and below the surface of the cell liquors. The dispersing means serves to mechanically diffuse the gaseous cell product into the cell liquor containing the reactant to provide intimate mixing and increased contact of reactants. The gasdispersing means may be any inert conventional absorption packing or distillation column packing such as, Berl saddles, Raschig rings, bubble trays, glass beads, and the like.

United States Patent [72] Inventors Edward H. Cook, Jr.;

Morris P. Grotheer, both of Lewiston, N.Y. [2i Appl. No. 755,845 [22] Filed Aug. 28, 1968 [45] Patented Oct. 26, 1971 [73] Assignee Hooker Chemical Corporation Niagara Falls, N.Y.

[54] ABSORPTION 0F GASEOUS CELL PRODUCT IN CELL LIQUOR APPARATUS 3 Claims, 1 Drawing Fig.

[52] US. (I 204/278, 204/81, 204/95, 204/258 [51] int. Cl 801k 3/00, C0 1 b 1 H26 [50] Field of Search 204/81, 96, 98, 257, 258, 264, 266, 278

[56] References Cited UNITED STATES PATENTS 583,718 6/1897 Teter 204/264 l,582,398 4/1926 l-lausmeister 204/278 2,763,607 9/l956 Staverman... 204/257 X 3,214,362 l0/l965 Juda 204/254 X 3,403,083 9/l968 Currey et al. 204/98 3,471,382 10/1969 Grother 204/98 Primary Examiner- F. C. Edmundson AnomeysPeter F. Casella, Donald C. Studley, Richard P.

Mueller, James F. Mudd and Richard K. Jackson ABSTRACT: The efficiency of electrolytic cells in which a gaseous cell product reacts with a component of the cell liquor or a reagent added to the electrolytic cell, may be substantially improved by the insertion of gas-dispersing means above the electrodes of the electrolytic cell and below the surface of the cell liquors. The dispersing means serves to mechanically diffuse the gaseous cell product into the cell liquor containing the reactant to provide intimate mixing and increased contact of reactants. The gas-dispersing means may be any inert conventional absorption packing or distillation column packing such as, Berl saddles, Raschig rings, bubble trays, glass beads, and the like.

time within the cell causing more of the hypochloride to be converted to chlorate within the cell. This-increased conversion within the cell decreases the amount of hypochlorate available for subsequent decay to produce oxygen and sodium chloride. This decay is one of the major inefficiencies in chlorate cells.

BACKGROUND FOR THE INVENTION Chemical reactions are frequently conducted within the confines of electrolytic cells. Generally a component product of electrolysis is caused to react with another reagent chemically within the electrolytic cell. Such reactions may be broadly grouped into electrolytic oxidations and addition-type reaction. The reactant which is caused to undergochemical reaction with the product of the electrolytic cell may in itself be part of the electrolyte within the cell or may be an added foreign reagent, such as, an olefin, acetylenic compound, an aliphatic hydrocarbon or halogenated hydrocarbon. For example, in a cell producing chlorine at an anode, chlorination reaction can occur within the electrolytic cell. Suchreactions include chlorination of olefin, acetylene, aliphatic hydrocarbon; a partially chlorinated hydrocarbon or any chemical compound normally considered to undergo chlorine substitution or chlorine addition. In addition, oxidation reaction where the sole function of the chlorine is to act as an oxidant.

Various methods have been used in the past to optimize the reaction between an electrolytic cell product and another reactant. conventionally, the cell product is removed from the cell and caused to react in a specially designed reactor where the conditions for reaction may be closely controlled. It is generally considered to be advantageous to avoid the necessity for complex costly chemical apparatus and to perform the reactions of electrolytic cell products, especially the gaseous products, as soon as possible so as to initiate the reaction while the gaseous reaction is still in a nascent or near nascent state.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the instant invention, there is provided an electrolytic cell wherein a compound is produced by chemical interaction between a gaseous electrolytic product and a reactant which is dissolved in the electrolyte of said cell or introduced into a reaction zonewithin the electrolyte. electrolyte. The electrolytic cell of the instant invention comprises a cell top, a cell bottom andsidewalls, electrodes comprising an anode and a cathode, means for conducting current to said cell, electrolyte feed means and withdrawal means, in which there is disposed above the cell electrodes but at least partially immersed beneath the top of the cell liquor a dispersing means which serves to break up and diffuse, large gas bubbles within the liquid phase of the cell contents.

The .gas dispersion means may be completely submerged below the upper level of the cell liquors, in which case it serves as packing to completely mix a gaseous cell product with the cell liquor or foreign reactant. In certain operations, it is desirable to only partially submerge the gas dispersion means below the upper level of the cell liquors. This manner of operation produces a twofold advantage. First, the gaseous cell product is intimately mixed with the cell liquors. Second, the portion of the dispersion means which extend above the top or upper level of the cell liquors acts as an antimisting shield. An additional advantage attributable to the electrolytic cell packing of the instant invention resides in an overall increase in the yield of the desired product within the cell itself.

By. increasing-the-in-cell production, the necessity for special retention tanks or external reaction vessels'is diminished as is the additional reaction time normally lost in completing reactions in extra-cell reactors.

The dispersing means disposed within the electrolytic may consist of packing material conventionally employed in absorption towers or distillation columns. For example, a packingwof'Berlsaddles Raschig rings, glass bead bubble trays or any known device for dispersing gases and liquids by mechanical diffusion which is inert toward the contents of the electrolytic cell,.may-constitute the dispersing means of the instant invention.

Electrolytic cells, either of the diaphragm or diaphragmless type may be provided with internal dispersing, means in accordance with this invention. The electrolytic cells may be of the monopolar or bipolar type.

DETAILED DESCRIPTION OF INVENTION For a complete understanding of the present invention, reference may be made to the accompanying drawing in which:

The FIGURE represents a side elevation partly in section of the electrolytic cell of this invention.

The electrolytic cell depictedin the FIGURE represents the conventional monopolar cell provided with a cell top 10 cell bottom 12 and internally a disposed anodes l4 cathodes 16. Cell 'feed inlet 22 provides for the introduction of electrolyte while gas vent 20 allows for the discharge of the gaseous electrol'ysis products and overflow outlet 28 provides liquid removal means. The dispersing means or absorption packing 18 which represents one aspect of this invention is disposed within the cell'top 10 on tray 30. The nonnal operating liquid and suspended gas level 24 exemplifies operation with absorp- 'tion packing l8 completely submerged in the electrolyte. The

gas-disengaging region within the electrolytic cell is shown 26.

In operation a suitable electrolyte is. introduced into the electrolytic cell through cell feed line 22. Current is introduced into the cell via current-conducting means (not shown) and the electrolyte within the cell is decomposed between anodes l4 and cathodes .16. The gaseous product of the'electrolysis, whether produced at the. anode or cathode, rises in the electrolytic cell, enters the region of the dispersing means or absorption packing 18 at which point large gas bubbles are finely dispersed and intimately mixed with a reactant within the cell, either foreign or inherent to the electrolyte, to produce a desired product. The product is withdrawn from the cell by overflow withdrawal means 28. Nonreactive gases continue to rise in the liquid electrolyte and form a relatively less dense liquid filled with suspended gas at 24, within cell top 10. The nonreactive gas disengages itself from liquid 24 filling space 26 and exiting cell top through gas vent 20.

When employing gas dispersion means in a conventional diaphragm-type electrolytic cell, where the chlorine generated at the anode is to react with an added reactant such as ethylene, propylene or butylene, the cell packing is placed above the anodes in the anolyte. The olefinmay be introduced into the cell via the cell feed inlet 22 or by way of a manifold injection system which inserts the gaseous olefin at a point below the packing in the cell. The gaseous olefin reacts with hypochlorous acid to form the corresponding halohydrin which in gaseous form exits the cell via vent 20. The halohydrin may be recovered from the other gaseous cell products by procedures known to the art.

The following examples are directed toward exemplification of the instant invention through illustration of the operation of an alkali metal chlorate cell. The conventional alkali metal chlorate cells are diaphragmless mono-[or bipolar cells. ln operation, an alkali metal chloride brine is fed to the elec trolytic cell. The application of a decomposition voltage, between the anode and cathode across the electrolyte, results in the production of chlorine at the anode and hydrogen plus hydroxy ions at the cathode. Chlorine within the aqueous elecevolved at the cathode intermingles with some of the gaseous anode product within the electrolyte and serves to entrain chlorine, which is carried with the hydrogen and vented from the conventional chlorate cell. By means of the instant invention, this conventionally lost chlorine value is recovered directly within the cell through reaction with water in the cell to produce more hypochlorous acid. This recovery occurs as a result of the disposition of absorption-packing or gasdispersing means above the electrodes of the cell.

EXAMPLE 1 An electrolytic cell capable of operating on approximately 55,000 amperes, equipped with graphite anodes and sheet steel cathodes was operated under conventional sodium chlorate producing conditions. The cell top was modified to provide a perforated shelf extending entirely over the surface area of the electrolyte. One-quarter-inch Berl saddles (3 inches deep) were placed on top of the perforated shelf to serve as gas-dispersing means. Under overwise equivalent conditions except for the perforated shelf and Berl saddles inside Table 1 Continued Average 5.85 3.24

0.9 Amperes per square inch 11.2 2.56 7.7 2.47 5.35

Average 8.08 2.51

The height of the absorption-packing or dispersing means within the electrolytic cell serves to increase the efiiciency of chlorine absorption within the cell.

EXAMPLE 1-6 An electrolytic cell comparable to that described in example 1 containing no diaphragm, equipped with graphite anodes and sheet steel cathodes, was employed in the production of sodium chlorate. The solution containing approximately 260 grams per liter sodium chloride, 100 grams per liter sodium chlorate and 2 grams per liter sodium dichromate was continuously electrolyzed in each of the following examples until the desired amount of sodium chlorate was produced. Sodium chloride brine was added as makeup during the course of the electrolysis. The cell operating temperature was between C. and C. The results of these experiments are tabulated in table 11. The current efficiencies shown in the table are based on chemical assay over the life of the experiment.

TABLE II Temper- Batch Current ature Flow assay density, range, rate, Final Final Hypocurrent Experiper Current degrees liters Cell NaCl, NuClO chlorite, emment Current square volume eenti- Ph per head, grams grams grams cieney, Number amperes ll'lCll ratio grade range minute inches per liter per liter per liter percent Remarks 1 260 0.6 3. 25 4145 7. 0-7. 5 1-1. 5 20 101 483 1. 4-3. 3 79. 0 No peeking. 2 340 0.8 4. 25 42-50 6.8-7.2 1 25 107 503 1. 2-3. 7 86. 4 Three inches packing above cell. 6 25 40-44 6. 9-7. 3 1, 4 25 162 344 1. 8-3. 1 87. 6 T t 1 .5 .9 87 n'eo inc 10s pnc 'ing.

llen ineies pnelfting 340 o. s 4. 25 4041 s. s-7. 0 4 25 160 340 1 5-2. 7 no. 2 Pm 4 insufficient because i 340 0. 8 4. 25 44-47 6. 6-7. 0 1-4 25 106 498 1. 1 2. 2 83. 7 J now through (.011

stopped on weekend. 5 340 0.8 8. 5 42-52 6. 77. 0 1. 4-2. 1 25 87 559 2. 1-2. 9 8!). 4 Ten inches packing. 6 340 0.8 16. 2 43-49 6.7-7. 1 1. 1-1. 6 21 92 520 1. 9-3. 7 8!). 3 Ten inches packing 'the cell top, the cell was operated to determine the relative .amount of chlorine recovered in the gas-dispersing region of Ethe cell. The results of this operation are presented in table 1.

lowered cell head.

Although chlorine losses during operation of the chlorate cells involved in the preceding experiments could be substantially eliminated by maintaining the electrolyte pH between 7 and 7.5, in this pH range more oxygen is produced at the anode and the overall current efficiency is only 79 percent (experiment 1). Therefore, for efi'lcient operation of this chlorate cell a lower pH range must be maintained in the electrolyte to avoid oxygen production of the anode.

In comparison with experiment 1, operating the electrolytic cell with a 3-inch layer of 74-inch Berl saddles placed in the electrolyte above the electrodes it was possible to operate the cell at a lower pH range (6.8 to 7.2) with lower chlorine losses than if absorption packing is absent. The height of the electrolyte was 25 inches while operating the cell with gasdispersing means. The combination of lower pH and the 3- inch packing above the electrodes resulted in increased current efficiency from 79 percent to between and 87 percent (experiments 2 and 3). Increasing the absorption packing height to 10 inches further increased the current efficiency to 90 percent over most of experiment 4. However, during the last days of experiment 4, the flow of brine to the cell was interrupted, causing a stagnant situation to develop. One nights operation at very low efficiency caused the overall batch efficiency to drop to 84 percent. Approximately 94 percent of the sodium chlorate produced in experiments 2 through 4 was produced inside the cell, as opposed to lower in-cell production followed by production in a conventional retention tank. Continuing with a -inch level of absorption packing, the current concentration of 340 amperes (0.8 amperes per square inch) was raised from 4.25 amperes per liter to 8.5 amperes per liter by decreasing the size of the retention tank. This resulted in an overall current efficiency of 89.4 percent (experiment 5) from electrolysis of the solution low in sodium chloride (87 grams per liter) with a high sodium chlorate (559 grams per liter) concentration.

In experiment 6, the current-volume ratio was further increased to 16.2 amperes per liter at thesame current density. An overall efiiciency of 89.3 percent was observed at a final sodium chloride concentration of 92 grams per liter and a final sodium chlorate concentration of 520 grams per liter.

With a 3-inch layer of packing, increasing current density from 0.6 to 0.8 amperes per square inch increased chlorine losses in the vent gases by about 1 percent. However, these losses were eliminated by increasing the absorption packing height to 10 inches. In the absence of the packing, chlorine losses varied from I to 12 percent. With 3 inches of packing, chlorine losses varied from 0.7 to 4 percent; and with 10 inches of packing the chlorine losses were below 2 percent at chlorate concentrations below 400 grams per liter. Higher chlorine losses were usually observed at chlorate concentrations above 400 grams per liter.

EXAMPLE 7 An electrolytic cell capable of operation on approximately 55,000 amperes and equipped with graphite anodes and steel cathode separated by an asbestos diaphragm was provided with 6 inches of packing in the cell top above the anodes in the anode compartment. The packing was below the surface of the anolyte within the anode compartment.

The cell was operated under normal conditions for the electrolysis of sodium chloride brine. Sodium chloride brine containing 300 grams per liter NaCl wu introduced into the anode compartment and a decomposition voltage was applied between the electrodes. Ethylene was continuously introduced into the anolyte below the lower level of the packing in stoichiometric excess.

The gaseous product recovered contained predominately ethylene chlorohydrin and small amounts of unreacted ethylene and ethylene dichloride.

What is claimed is:

1. an electrolytic cell comprising a cell housing, anodes and cathodes disposed within said cell housing, means for introducing a liquid electrolyte into said cell housing, so as to form and maintain a body of electrolyte within said housing in contact with said anodes and cathodes but having an upper surface which is above said anodes and cathodes, means for applying an electrical potential between said anodes and cathodes to decompose said electrolyte and form decomposition products, at least one of which is gaseous, means for conducting reaction products from said cell housing, and means for dispersing said gaseous decomposition products within said liquid electrolyte, said dispersion means comprising a layer of inert packing material, which layer is pervious to gas and disposed within said cell housing so as to be at least partially below the upper surface of the body of electrolyte formed within said cell housing but completely above all said anodes and cathodes.

2. The electrolytic cell as claimed in claim 1 wherein the layer of inert packing material which forms the gas dispersion means is selected from Berl saddles, Raschig rings, bubble trays, and glass heads.

3. The electrolytic cell as claimed in claim 2 wherein the gas-dispersing means is disposed within the cell housing so as to be completely below the upper surface of the body of electrolyte formed within the cell housing.

PO-YWF UNITED STATES PATENT GFFECE CERTIFICATE OF CORRECTION Patent No. 3,616,443 Dated October 26, 1971 Inventor(s) Edward H. Cook, Jr. et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- Column 1, lines 54 and 55, "electrolyte.electrolyte." -1

should be ---e1ectrolyte.- Column 6, after line 9, the following should be inserted as a new paragraph, ---Having disclosed the invention, it will be apparent to those given the art that it is applicable to any electrolytic process in which a gaseous product of the electrolysis is intentionally caused to react with another reactant within the electrolytic cell. Thus, although the specific examples presented in this application are directed toward alkali metal chlorate production these examples are presented as representative embodiments of the invention rather than limitations on the scope of the invention.--; line ll, "an" should be --An--.

Signed and sealed this 25th day of Aprili972.

(SBAL) Attest:

EDWARD M.FLMTCHER,JH. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. The electrolytic cell as claimed in claim 1 wherein the layer of inert packing material which forms the gas dispersion means is selected from Berl saddles, Raschig rings, bubble trays, and glass beads.
 3. The electrolytic cell as claimed in claim 2 wherein the gas-dispersing means is disposed within the cell housing so as to be completely below the upper surface of the body of electrolyte formed within the cell housing. 